The IEEE 802.3af standard defines a mechanism to deliver power to an Ethernet device via the Ethernet wire, known as “Power Over Ethernet” or PoE. FIG. 1 depicts a typical IEEE 802.3af setup in which power is delivered to a powered device (“PD”) 10 (right side Ethernet device) from a power sourcing equipment (“PSE”) 11 over a category 5 Ethernet cable 12. The power delivery may be using the data copper wire pairs (mode A) or the unused copper wire pairs (mode B). The left side Ethernet device 11 is not powered by PoE; it draws power from another source. It is the PSE device 11 that decides which wires to use (mode A or mode B). A typical mid-span is injector (where the PSE 11a is separate from the Ethernet device 11b) usually uses mode B, while a device that embeds a PSE typically uses mode A.